Monopolar instruments, wherein the treatment current is introduced into the tissue via a neutral electrode and flows through the body, are used, amongst other things, during electrosurgical interventions. Such an arrangement is illustrated in FIGS. 1 and 2. The instrument comprises a generator 1, which supplies a high frequency electrical current (normally 350 kHz), to which an electrosurgical instrument 2 and a neutral electrode 3 are connected. Neutral electrode 3 is affixed with an intermediate layer of a conductive gel to a skin layer of a patient to be treated.
EP 1 173 095 B1 discloses a neutral electrode which has a construction corresponding to that according to FIGS. 1 and 2. Neutral electrode 3 has a backing foil 9 to which is attached a main electrode 10 that may be connected to generator 1 via a terminal lug 13. An electrically conductive ring 11 is provided around main electrode 10 and is separated from main electrode 10 by a gap 12. The electrically conductive ring 11 leads to an improved current distribution on the skin section contacted or on the tissue situated beneath it. It should be noted that the various types of tissue have very different specific resistances. For example, muscles have a specific resistance of 0.2 mΩcm (at 1 MHz), whereas the specific resistance of blood is 0.16 mΩcm and that of fat is 3.3 mΩcm. Furthermore, the affixed neutral electrodes may also easily become detached, especially around the edges such that contact is interrupted in places.
Many suggestions have been made to determine correct seating of the electrode. For example, in EP 0 390 937 B1 a device for monitoring the application of neutral electrodes during high frequency surgery is proposed wherein work is carried out using two electrodes of equal size and a differential resistance is measured between the two electrodes. Correct or faulty seating of the electrode is deduced from the measured result.
EP 1 051 949 B1 discloses a neutral electrode with an impedance measuring device, however, it is not possible to infer precise directions for the construction of such an electrode from this printed publication.
In all cases, known electrode construction and methods are only suitable to a limited degree for ensuring correct introduction of a high frequency treatment current by way of a neutral electrode with justifiable expenditure.
Thus, the object of the disclosed embodiments is to provide an electrode device and a method for monitoring the contact and the high frequency current flow and its spatial distribution such that increased safety is ensured due to improved current introduction properties.